This invention relates to a hemming machine for forming an automobile door, for example, by bending a flange part of an outer panel along its outer periphery towards an inner panel appropriately positioned with respect to it and bonding them together.
Prior art hemming machines of this type are generally provided separately with a preliminary bending block for a preliminary bending process and a final bending block for a final bending process. The preliminary bending block is deployed first to preliminary bend the flange part of the outer panel by a specified angle towards the inner panel. The preliminary bending block is then retracted because it would otherwise be in the way of the next operation. Thereafter, the final bending block is deployed to bend further the preliminary bent flange part of the outer panel until it comes into contact with the inner panel. Provided separately with a block dedicated for carrying out the preliminary bending and another block dedicated for carrying out the final bending which can be independently operated, hemming machines of this type are advantageous in that the preliminary bending and the final bending of the flange part of the outer panel can be both effected in specified ways. On the other hand, there are disadvantages in that two bending blocks are separately required, each requiring its own operating mechanism and hence that the machine as a whole becomes large, its structure becomes complicated and the cost of its production becomes higher.
In view of these problems, Japanese Patent Publications Tokkai 55-122636 and 56-14030 disclosed hemming machines of the type having a single bending block integrating both a preliminary bending surface and a final bending surface, the block being caused to move on an arcuate path around a certain selected axis such that the flange part of the outer panel is initially bent towards the inner panel by a specified angle by the preliminary bending surface at a forward position on the bending block and then until it contacts the inner panel by the final bending surface at a backward position. Requiring only one bending block and one driving mechanism for its operation, hemming machines of this type are advantage in that the machine as a whole can be compactly formed, its structure is simpler and its production cost is lower. With prior art hemming machines of this type, however, it is difficult to apply appropriate compressive forces on the flange part of the outer panel at both times of the preliminary bending and the final bending because both are carried out by moving the same single bending block on an arcuate path around the same axis. Since the flange part on the outer panel is subjected to a force with an inappropriate perpendicular component at the time of its preliminary bending, the rising portion of the flange becomes easily distorted. A force with an unreasonable horizontal component which acts on the flange at the time of its final bending, furthermore, tends to distort the main part of the outer panel.
It is therefore an object of this invention to provide an improved hemming machine which is compact as a whole, simple in structure, and inexpensive to produce but does not cause distortion of the outer panel at the times of preliminary bending and final bending.
A hemming machine embodying this invention, with which the above and other objects can be accomplished, may be characterized as comprising a single bending block having a surface (herein referred to as xe2x80x9cthe preliminary bending surfacexe2x80x9d to be used for carrying out a preliminary bending process) and another surface (herein referred to as xe2x80x9cthe final bending surfacexe2x80x9d to be used for carrying out a final bending process), a lower block for placing thereon an outer panel with a flange (with an inner panel positioned on the outer panel) and a mechanism for moving the bending block in an arcuate way around a specified axis such that a force with a relatively large horizontal component is applied to the flange of the outer panel when the preliminary bending surface of the bending block bends the flange in the preliminary bending process, and then in another arcuate way around another axis such that a force with a relatively large perpendicular component is applied to the flange of the outer panel when the final bending surface of the bending block bends the flange in the final bending process.